The finding is significant because such a drug could combat frailty, which often limits physical activities of older people.

The study, to be published in the April issue of the Journal of Clinical Endocrinology & Metabolism, says older adults have reduced growth hormone production as they age.

"As we age, decreased strength and physical agility trigger a cascade of events leading to loss of independence and disability," says study author Heidi K. White, MD, MHS, an associate professor of medicine at Duke. "By boosting the production of growth hormone, we may be able to slow this process and help people lead active lives longer."

The researchers studied 395 men and women ages 65 to 84 with mild functional limitations. Some took placebos, and others took one of four doses of a drug called capromorelin, developed by Pfizer.

After a year, participants who took various doses of capromorelin increased growth hormone production, and researchers recorded increases in lean body mass and body weight. The researchers say the participants also registered improvements in two physical performance tests: stair climbing and heel-to-toe walking.

White describes the results as promising but "relatively mild" and says more research is needed. Researchers analyzed other studies that looked at the effect of exercise on older people, which also improved physical abilities.

White says capromorelin could be used in combination with exercise to improve physical capabilities of older people.

The scientists write that their work confirms previous research that found that growth hormones and its stimulators, including one called MK-677, also can strengthen older people.

The latest study was funded by Pfizer Global Research and Development. All of the researchers acknowledged receiving funds or having some other financial relationship with Pfizer, either currently or in the past.